This invention lies in the field of appparatus for raising, lowering, and transfering nuclear fuel assemblies and accessories. It is directed more particularly to such an apparatus which is constructed and arranged to pick up, transfer, and deposit a fuel assembly, or a control rod bundle, or both, either separately or with the control rods in place in the fuel assembly. It is also directed to such an apparatus which, with the same mechanism, can handle an orifice rod bundle with minimum vertical travel in minimum time.
As is well known, nuclear power reactors include a suitable reactor core and a plurality of fuel assemblies mounted in the core in parlallel vertical juxtaposition. Some portions of some assemblies contain control rods and some contain orifice rods, in each case the rods being secured to a head which enables them to be deposited or removed in a group. On occasion, poison rods and shaping rods are used and are connected to heads in the same general way. The basic control rods, poison rods, and shaping rods are all long, nearly the length of the tube elements of the fuel assemblies, while the orifice rods are very short and have a length which is only a small percentage of the length of the other rods. Since they all exert some controlling function they may all be considered as control rods for the general discussion of the disclosure.
The nuclear fuel located in the lower ends of the fuel assemblies gradually becomes depleted through use. When the fuel is exhausted a fuel assembly is removed from the core and transferred to a storage location where a fresh assembly may be available to replace it or it may be recharged. If the fuel is only partially spent, an assembly may be transferred to a different position in the core. In some cases rod bundles may be replaced or transferred from one assembly to another. In conventional practice, using a standard handling bridge, a separate mast depending from the bridge is used to transfer the fuel assembly, the long rods, and the short rods. This requires a large and cumbersome apparatus, and locating and operating each separate mast consumes a great deal of time. Since there are a large number of fuel assemblies in each core, the time consumed is very great and of course the reactor is out of service during the entire transfer period. Consequently it is highly desirable to make use of any apparatus which will reduce the down time by a substantial extent.